(a) Technical Field of the Invention
The present invention relates to a photosensitive material for electrophotography. More particularly, the present invention relates to an electrophotographic photosensitive material repeatedly usable by a PPC copier, laser beam printer, digital copier or the like, the intermediate layer of which is improved.
(b) Description of the Prior Art
Generally, a repeatedly usable photosensitive material (hereinafter referred to simply as "photosensitive material") has an intermediate layer comprising a resin of a relatively low resistance between a substrate and a photosensitive layer in order to obtain a favorable electrostatic property (to block the injection of unnecessary electric charge and to maintain an appropriate charge acceptance) and further to improve the adhesive property of the photosensitive layer with the substrate.
Examples of a resin conventionally used for the intermediate layer include (i) a water soluble resin such as casein, polyvinyl alcohol and the like, (ii) a polyamide resin such as nylon, copolymerized nylon and the like, (iii) light-curable or thermosetting resins, and the like. However, the conventional photosensitive material, the intermediate layer of which is made from the above mentioned resins, has disadvantages such as the residual potential increasing because the intermediate layer becomes highly resistant at a low moisture, and, as a consequence that the sensitivity of the photosensitive material is lowered.
There were various methods proposed to remove the above mentioned disadvantages, for example, adding an electroconductive pigment such as indium oxide, tin oxide, carbon and the like to the intermediate layer (see Japanese Patent Laid Open No. 58-93063) or adding an electroconductive polymer to the intermediate layer (see Japanese Patent Laid Open No. 58-95744). However, these methods still have some problems for practical use. For example, in the former method, it was necessary to form a second intermediate layer consisting of a resin only between the photosensitive layer and the intermediate layer containing the electroconductive pigment in order to prevent the electrostatic property of the photosensitive material from lowering. In the latter method, the sensitivity is lowered although the electrostatic property does not degrade too much.
In the case of a multi-layered type photosensitive material, the photosensitive layer of which is formed by laminating a charge generating layer and a charge transfer layer, the moire phenomenon often occurs between a substrate and the surface of the charge transfer layer by multi-reflection. In order to prevent the occurrence of the moire phenomenon, it has been proposed to add a light-dispersing material to an intermediate layer. However, even in the case of this photosensitive material, the electrostatic property is lowered and the residual potential is increased during repeated use. Thus, this photosensitive material also needs to be improved.